150+ Switch Gear and Protection Solved MCQs

1.

The main function of a fuse is to

A. protect the line
B. open the circuit
C. protect the appliance
D. prevent excessive currents
Answer» D. prevent excessive currents
2.

On which of the following routine tests are conducted?

A. Oil circuit breakers
B. Air blast circuit breakers
C. Minimum oil circuit breakers
D. All of the above
Answer» D. All of the above
3.

SF6 gas

A. is yellow in colour
B. is lighter than air
C. is nontoxic
D. has pungent small
Answer» C. is nontoxic
4.

The arcing contacts in a circuit breaker are made of

A. copper tungsten alloy
B. porcelain
C. electrolytic copper
D. aluminium alloy
Answer» A. copper tungsten alloy
5.

Which of the following medium is employed for extinction of arc in air circuit breaker ?

A. Water
B. Oil
C. Air
D. SF6
Answer» C. Air
6.

With which of the following, a circuit breaker must be equipped for remote operation ?

A. Inverse time trip
B. Time-delay trip
C. Shunt trip
D. None of the above
Answer» C. Shunt trip
7.

Fault diverters are basically

A. fuses
B. relays
C. fast switches
D. circuit breakers
Answer» C. fast switches
8.

A thermal protection switch can protect against

A. short-circuit
B. temperature
C. overload
D. over voltage
Answer» C. overload
9.

Arc in a circuit behaves as

A. a capackive reactance
B. an inductive reactance
C. a resistance increasing with voltage rise across the arc
D. a resistance decreasing with voltage rise across the arc
Answer» D. a resistance decreasing with voltage rise across the arc
10.

Thermal circuit breaker has

A. delayed trip action
B. instantaneous trip action
C. both of the above
D. none of the above
Answer» A. delayed trip action
11.

Relays can be designed to respond to changes in

A. resistance, reactance or impedance
B. voltage and current
C. light intensity
D. all above
Answer» D. all above
12.

Overload relays are of…… type.

A. induction
B. solid state
C. thermal
D. all above
Answer» D. all above
13.

Thermal overload relays are used to protect the motor against over current due to

A. short-circuits
B. heavy loads
C. grounds
D. all of the above
Answer» B. heavy loads
14.

Magnetic circuit breaker has ______ trip action.

A. delayed
B. instantaneous
C. both of the above
D. none of the above
Answer» B. instantaneous
15.

D.C. shunt relays are made of

A. few turns of thin wire
B. few turns of thick wire
C. many turns of thin wire
D. many turns of thick wire
Answer» C. many turns of thin wire
16.

The relay operating speed depends upon

A. the spring tension
B. the rate of flux built up
C. armature core air gap
D. all of the above
Answer» D. all of the above
17.

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

A. have low contact resistance
B. be clean and smooth
C. be of sufficient size and proper shape
D. have all above properties
Answer» D. have all above properties
18.

Circuit breakers usually operate under

A. transient state of short-circuit current
B. sub-transient state of short-circuit current
C. steady state of short-circuit current
D. after D.C. component has ceased
Answer» A. transient state of short-circuit current
19.

Circuit breakers are essentially

A. current carrying contacts called electrodes
B. arc extinguishers
C. circuits to break the system
D. tr
Answer» A. current carrying contacts called electrodes
20.

The current zero interruption, in oil and air blast circuit breakers, is achieved by

A. lengthening of the gap
B. cooling and blast effect
C. both (a) and (b)
D. deionizing the oil with forced air
Answer» C. both (a) and (b)
21.

Air blast circuit breaker is used for

A. over currents
B. short duty
C. intermittant duty
D. repeated duty
Answer» D. repeated duty
22.

An efficient and a well designed protective relaying should have

A. good selectivity and reliability
B. economy and simplicity
C. high speed and selectivity
D. all of the above
Answer» D. all of the above
23.

Burden of a protective relay is the power

A. required to operate the circuit breaker
B. absorbed by the circuit of relay
C. developed by the relay circuit
D. none of the above
Answer» B. absorbed by the circuit of relay
24.

Directional relays are based on flow of

A. power
B. current
C. voltage wave
D. all of the above
Answer» A. power
25.

A differential relay measures the vector difference between

A. two currents
B. two voltages
C. two or more similar electrical quantities
D. none of the above
Answer» C. two or more similar electrical quantities
26.

A transmission line is protected by

A. inrush protection
B. distance protection
C. time graded and current graded over current protection
D. both (b) and (c)
Answer» D. both (b) and (c)
27.

Large internal faults are protected by

A. merz price percentage differential protection
B. mho and ohm relays
C. horn gaps and temperature relays
D. earth fault and positive sequence relays
Answer» A. merz price percentage differential protection
28.

When a transmission line is energized, the wave that propagates on it is

A. current wave only
B. voltage wave only
C. both (a) and (b)
D. power factor wave only
Answer» C. both (a) and (b)
29.

Protective relays are devices that detect abnormal conditions in electrical circuits by measuring

A. current during abnormal condition
B. voltage during abnormal condition
C. constantly the electrical quantities which differ during normal and abnormal conditions
D. none of the above
Answer» C. constantly the electrical quantities which differ during normal and abnormal conditions
30.

The voltage appearing across the contacts after opening of the circuit breaker is called______voltage.

A. recovery
B. surge
C. operating
D. arc
Answer» A. recovery
31.

Ionization in circuit breaker is facilitated by

A. high temperature
B. increase of mean free path
C. increasing field strength
D. all of the above
Answer» D. all of the above
32.

In a circuit breaker the basic problem is to

A. maintain the arc
B. extinguish the arc
C. transmit large power
D. emit the ionizing electrons
Answer» C. transmit large power
33.

Overheating of relay contacts or contact born out is due to

A. slow making and breaking of load circuit contacts
B. foreign matter on the contact surface
C. too low contact pressure
D. all of the above
Answer» D. all of the above
34.

Interruption of large currents by relay requires

A. arc suppressing blow out coils
B. wide separation of the opened contacts
C. high speed opening of contacts
D. all of the above
Answer» D. all of the above
35.

Shunt capacitance is neglected while considering

A. short transmission line
B. medium transmission line
C. long transmission line
D. medium and long tr
Answer» A. short transmission line
36.

The arc voltage produced in A.C. circuit breaker is always

A. in phase with the arc current
B. lagging the arc current by 90″
C. leading the arc current by 90°
D. none of the above
Answer» A. in phase with the arc current
37.

The time of closing the cycle, in modern circuit breakers is

A. 0.003 sec
B. 0.001 sec
C. 0.01 sec
D. 0.10 sec
Answer» A. 0.003 sec
38.

Insulation resistance of high voltage circuit breakers is more than

A. 1 mega ohms
B. 10 mega ohms
C. 100 mega ohms
D. 500 mega ohms
Answer» C. 100 mega ohms
39.

H.R.C. fuses provide best protection against

A. overload
B. reverse current
C. open-circuits
D. short-circuits
Answer» D. short-circuits
40.

The ground wire should not be smaller than No ______ copper.

A. 2
B. 4
C. 6
D. 10
Answer» D. 10
41.

The delay fuses are used for the protection of ________ .

A. motors
B. power outlet circuits
C. fluorescent lamps
D. light circuits
Answer» A. motors
42.

Which of the following is the least expensive protection for overcurrent is low voltage system ?

A. Rewireable fuse
B. Isolator
C. Oil circuit breaker
D. Air break circuit breaker
Answer» A. Rewireable fuse
43.

Resistance grounding is used for voltage between

A. 33kVto66kV
B. HkVto33kV
C. 3.3kVandllkV
D. none of the above
Answer» C. 3.3kVandllkV
44.

The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to

A. lubricate the contacts
B. insulate the contacts from switch body
C. extinguish the arc
D. all of the above
Answer» C. extinguish the arc
45.

In Railway applications ______ circuit breaker is used.

A. SFe
B. bulk oil
C. minimum oil
D. air break
Answer» D. air break
46.

To protect most of the electrical equipment handling low power, the types of relays used are

A. thermocouple
B. electronic and bimetallic
C. both (a) and (b)
D. none of the above
Answer» C. both (a) and (b)
47.

Wave trap is used to trap waves of

A. power frequencies
B. higher frequencies entering generator or transformer units
C. either of the above
D. none of the above
Answer» B. higher frequencies entering generator or transformer units
48.

Ungrounded neutral transmission system is not recommended because of system

A. insulation being overstressed due to over voltages
B. insulation overstress may lead to failure and subsequent phase to phase faults
C. being inadequately protected against ground fault
D. all of the above
Answer» D. all of the above
49.

The reflection co-efficient at the open circuited end of a transmission line.

A. zero
B. infinity
C. unity
D. none of the above
Answer» C. unity
50.

For the protection of power station buildings against direct strokes the requirements are

A. interception
B. interception and conduction
C. interception, conduction and dissipation
D. interception, conduction, dissipation and reflection
Answer» C. interception, conduction and dissipation
51.

The line insulation is the insulation level of the station equipment.

A. less than
B. same as
C. more than
D. not directly related with
Answer» D. not directly related with
52.

The interaction between a transmission line and communication line is minimized by

A. transposing transmission as well as communication lines
B. increasing the height of the trans-mission line tower
C. increasing the distance between the two lines
D. all of the above
Answer» D. all of the above
53.

When a wave propagates on a transmission line, it suffers reflection several times at

A. tapping
B. load end
C. sending end
D. sending and other end
Answer» D. sending and other end
54.

Which of the following statements is incorrect?

A. Station batteries are used to operate relay only
B. The lightning arresters are basically surge diverters
C. An impedance relay has maximum fault current when fault occurs near the relay
D. A high speed relay has an operation of 1 to 2 cycles
Answer» A. Station batteries are used to operate relay only
55.

Discrimination between main and back up protection is provided by the use of relays which are

A. fact
B. sensitive
C. slow
D. none of the above
Answer» C. slow
56.

Induction cup relay is operated due to changes in

A. current
B. voltage
C. impedance
D. all of the above
Answer» D. all of the above
57.

A.C. network analyser is used to solve problems of

A. load flow
B. load flow and short-circuit
C. load flow and stability
D. load flow, short-circuit and stability
Answer» D. load flow, short-circuit and stability
58.

Which of the following statements is incorrect ?

A. Lightning arrestors are used before the switchgear
B. Shunt reactors are used as compensation reactors
C. The peak short current is (1.8 xV2) times the A.C. component
D. The MVA at fault is equal to base MVA divided by per unit equivalent fault reactance
Answer» A. Lightning arrestors are used before the switchgear
59.

Short-circuit currents are due to

A. single phase to ground faults
B. phase to phase faults
C. two phase to ground faults
D. any of these
Answer» D. any of these
60.

To reduce short circuit fault currents are used.

A. reactors
B. resistors
C. capacitors
D. none of the above
Answer» A. reactors
61.

Bus coupler is very essential in arrangement

A. single bus
B. double bus, double breaker
C. main and transfer bus
D. all of the above
Answer» C. main and transfer bus
62.

For cost and safety, the outdoor substations are installed for voltages above

A. 11 kV
B. 33 kV
C. 60kV
D. 110kV
Answer» B. 33 kV
63.

The short circuit in any winding of the transformer is the result of

A. mechanical vibration
B. insulation failure
C. loose connection
D. impulse voltage
Answer» D. impulse voltage
64.

relays are used for phase faults on long line.

A. Impedance
B. Reactance
C. Either of the above
D. None of the above
Answer» A. Impedance
65.

For which of the following protection from negative sequence currents is provided?

A. Generators
B. Motors
C. Transmission line
D. Tr
Answer» A. Generators
66.

relay is preferred for phase fault on short transmission line.

A. Induction type
B. Reactance
C. Impedance
D. None of the above
Answer» B. Reactance
67.

Distance relays are generally

A. split-phase relays
B. reactance relays
C. impedance relays
D. none of the above
Answer» D. none of the above
68.

For which of the following ratings of the transformer differential protection is recommended ?

A. above 30 kVA.
B. equal to and above 5 MVA
C. equal to and above 25 MVA
D. none of the above
Answer» B. equal to and above 5 MVA
69.

A _______ is used to measure the stator % winding temperature of the generator.

A. thermocouple
B. pyrometer
C. resistance thermometer
D. thermometer
Answer» C. resistance thermometer
70.

The under voltage relay can be used for

A. generators
B. busbars
C. transformers
D. all of the above
Answer» D. all of the above
71.

The relay with inverse time characteristic will operate within

A. 1.5 sec
B. 5 to 10 sec
C. 5 to 20 sec
D. 20 to 30 sec
Answer» B. 5 to 10 sec
72.

The single phasing relays are used for the protection of

A. single phase motors only
B. two phase motors only
C. two single phase motors running in parallel
D. three phase motors
Answer» D. three phase motors
73.

Which of the following devices will receive voltage surge first travelling on the transmission line ?

A. Lightning arresters
B. Relays
C. Step-down transformer
D. Switchgear
Answer» A. Lightning arresters
74.

Which of the following parameter can be neglected for a short line ?

A. Inductance
B. Capacitance
C. Resistance
D. Reactance
Answer» B. Capacitance
75.

Series reactors should have

A. low resistance
B. high resistance
C. low impedance
D. high impedance
Answer» A. low resistance
76.

Which of the following circuit breakers has high reliability and minimum maintenance ?

A. Air blast circuit breakers
B. Circuit breaker with SF6 gas
C. Vacuum circuit breakers
D. Oil circuit breakers
Answer» B. Circuit breaker with SF6 gas
77.

Arc in a circuit breaker is interrupted at

A. zero current
B. maximum current
C. minimum voltage
D. maximum voltage
Answer» A. zero current
78.

transmission line has reflection coefficient as one.

A. Open circuit
B. Short-circuit
C. Long
D. None of the above
Answer» A. Open circuit
79.

What will be the reflection co-efficient of the wave of load connected to transmission line if surge impedance of the line is equal to load ?

A. Zero
B. Unity
C. Infinity
D. None of the above
Answer» A. Zero
80.

The inverse definite mean time relays are used for over current and earth fault protection of transformer against

A. heavy loads
B. internal short-circuits
C. external short-circuits
D. all of the above
Answer» B. internal short-circuits
81.

Over voltage protection is recommended for

A. hydro-electric generators
B. steam turbine generators
C. gas turbine generators
D. all of the above
Answer» D. all of the above
82.

Air blast circuit breakers for 400 kV power system are designed to operate in

A. 100 microsecond
B. 50 millisecond
C. 0.5 sec
D. 0.1 sec
Answer» B. 50 millisecond
83.

Overfluxing protection is recommended for

A. distribution transformer
B. generator transformer of the power plant
C. auto-transformer of the power plant
D. station tr
Answer» A. distribution transformer
84.

Series capacitors are used to

A. compensate for line inductive reactance
B. compensate for line capacitive reactance
C. improve line voltage
D. none of the above
Answer» A. compensate for line inductive reactance
85.

Admittance relay is _______ relay.

A. impedance
B. directional
C. non-directional
D. none of the above
Answer» B. directional
86.

The material used for fuse must have

A. low melting point and high specific resistance
B. low melting point and -low specific resistance
C. high melting point and low specific resistance
D. low melting point and any specific resistance
Answer» A. low melting point and high specific resistance
87.

If the fault occurs near the impedance relay, the VII ratio will be

A. constant for all distances
B. lower than that of if fault occurs away from the relay
C. higher than that of if fault occurs away from the relay
D. none of the above
Answer» B. lower than that of if fault occurs away from the relay
88.

The torque produced in induction type relay (shaded pole structure) is

A. inversely proportional to the current
B. inversely proportional to the square of the current
C. proportional to the current
D. proportional to square of the current
Answer» B. inversely proportional to the square of the current
89.

The steady state stability of the power system can be increased by

A. connecting lines in parallel
B. connecting lines in series
C. using machines of high impedance
D. reducing the excitation of machines
Answer» A. connecting lines in parallel
90.

The inductive interference between power and communication line can be minimized by

A. transposition of the power line
B. transposition of the communication line
C. both (a) and (b)
D. increasing the distance between the conductors
Answer» C. both (a) and (b)
91.

The power loss is an important factor for the design of

A. transmission line
B. motor
C. generator
D. feeder
Answer» A. transmission line
92.

A fuse is connected

A. in series with circuit
B. in parallel with circuit
C. either in series or in parallel with circuit
D. none of the above
Answer» A. in series with circuit
93.

H.R.C. fuse, as compared to a rewirable fuse, has

A. no ageing effect
B. high speed of operation
C. high rupturing capacity
D. all of the above
Answer» D. all of the above
94.

The fuse rating is expressed in terms of

A. current
B. voltage
C. VAR
D. kVA
Answer» A. current
95.

The fuse blows off by

A. burning
B. arcing
C. melting
D. none of the above
Answer» C. melting
96.

On which of the following effects of electric current a fuse operates ?

A. Photoelectric effect
B. Electrostatic effect
C. Heating effect
D. Magnetic effect
Answer» C. Heating effect
97.

An isolator is installed

A. to operate the relay of circuit breaker
B. as a substitute for circuit breaker
C. always independent of the position of circuit breaker
D. generally on both sides of a circuit breaker
Answer» D. generally on both sides of a circuit breaker
98.

A fuse in a motor circuit provides protection against

A. overload
B. short-circuit and overload
C. open circuit, short-circuit and overload
D. none of the above
Answer» B. short-circuit and overload
99.

Protection by fuses is generally not used beyond

A. 20 A
B. 50 A
C. 100 A
D. 200 A
Answer» C. 100 A
100.

A fuse is never inserted in

A. neutral wire
B. negative of D.C. circuit
C. positive of D.C. circuit
D. phase dine
Answer» A. neutral wire
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